Loud-speaking telephone receiver



Jan. 11, 1927. A. THQMAS LOUD SPEAKING TELEPHONE RECEIVER Filed 1923 2Sheets-Sheet 1 5 ./s I I INVENTOR Jan. '11, 1927. I A THOMAS 1,614,327

' LOUD SPEAKING TELEPHONE RECEIVER Filed Dec. 14,1925 2 Sheets -Sheet 2Patented Jam-.11, 1927.

UNlTED STATES; PATENT Q'OFFIICE'.

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i LO UD SBEAKING rarnrnonn necmvriar Application filed December14,1e'2sj. Serial no, 680,597.

My invention relates to telephone instruments. and its main object is toprovide a loudspeaking receiver-particularly adapted for use. in radioreception, although not limited to this field.

One of the main sources of trouble encountered in theoperation' of radioloudspeakers heretofore on the market, is due to the armature ordiaphragnrof the magnet striking the pole pieces when the air gap isadjusted too close. To obtain .a strong re- .production through thesep'riordevices. it is necessary to adjust the armature or diaphragm asclosely as possible to the magnetic pole pieces, but, when that is done,the armatureior diaphragm is liable to strike the pole pieces when astrong current passes through the speaking coil. -.'1he result is adistortedreproduction. On the other hand, .when the air gap between themagnet and its armature (or diaphragm) is increased so as to avoid-thedanger of the armature striking the pole pieces. the effect of thecurrent in the coil isiweakened, and the resultant reproduction iscorrespondingly feeble.

One of the main purposes of my invention is to overcome the foregoingdefects and difliculties in prior loudspeakers'and to this end Ihaveprovided a l'oudspeaking telephone receiver in which themagneticefi'ect of the coil on the armature may bevaried independently of theairgap between the armature and the pole pieces. This regulation of themagnetic efiiechof the speaking coil, as I may call it. is accomplishedby varying the reluctance of the magnetic path.

of the flux set up by the current in the coil. One of the simplest waysof varying this magnetic reluctance is to provide an adjust- T able ironcore for the coil. In the practical embodiment, which I preferat thepresent time, thecore Oftll coil is made in two sections. one of whichis adjustable with respect to the other, so that the sections may eitherbe brought closely together, to form a continuous core, or may beseparated by an air gap. By simply ad ust1 ng-th1sa1r gap,

I the magnetic effect of the coil on the armature is varied accordingly,'without varying or disturbing the air. gap between ture and the polepieces. f

In accordance with a further feature of be used like a the arma myinvention." I provide magnet in which one orboth of the polepieces arebifurcated and the bifurcations of each polepiece are featurepreviously.

correspondingly increased or diminished efiect.- A Myinvention -furthercomprises improved means for mounting the operative parts in a readilyaccessible position within an outer;

casing, WhlClI is adapted to carry a horn and be supported on a stand,or which may for connection with a fixed horn,

cabinet;

phonograph horn enclosed in a The foregoing and other objects and ad Ivantages of my invention will become clear from a detailed descriptionof the accompa-nyingv drawings. which show my invention in twoillustrative embodiments. In thesedrawings- Fig'l isatransverse crosssection on line 1-1 of Fig. 2, showing a loudspeaking telewith myinvention; p

Fig. 2 is a top plan view in section; proximately on the broken line 2-2i Fig. 3 is an enlargedfragmentary View in cross-section. approximatelyon line 33 .phone receiver constructed in accordance of Fig. 2, showingmeans for adjusting the. 7

air. gap .in the core of the coil:

Fig, 4 is a cross-sectionv on line 4-4 of Fig. a

Fig. 5 is a detached perspective view of operative parts in the.construction shown in Figs. 1 and 2; v

Fig.6 is a; fragmentary view'jin crosssection o'n line 66 of Fig. 2EFig. 7"is a fragmentaryview in crosssection on line. 7-7 ofFig. 2;.

Fig. 8 isan enlarged fragmentary view the casting which directlysupports the:.

loo

of an adjustable connection between the armature and the diaphragm forvarying the veffective leverage between the two;

or supportindicated as a whole by B, as

' pole pieces best shown in Fig. 5. This support, which may convenientlybe cast or molded out of suitable non magnetic material, such' asaluminum orbakelite, consists of a circular base 1, airing 2, andconnecting posts 3. If desired, these parts may be made separate andrigidly secured together, but'it is preferable to mold or cast them in asingle rigid piece. So it will be understood that when I refer to thepart It as a. casting, I use the term merely for convenience.

-On base 1 are mounted two permanent steel magnetsM and M, which areoppositely arranged and suitably spaced from each other at their polarends. The magnets. are firmly held on base 1 in any practical way, as byscrews :12 passing through the base into the magnets. magnets are soarranged that their like poles lie opposite each other. Tothepoles- Nand S of magnet M are secured 4 Y ole pieces 4 and 5, and to the polesNand g of magnet M are secured pole pieces 4 and 5'.

These pole pieces are refe'rably of soft iron,

or other material of iigh' magnetic permeability. Any suitable means maybe used for holding the pole pieces infirm contact with the magnets. Inthe drawings I have shown the polepieces attached directly to the polarends of theniagnets by screws 6.

As seen in Fig. 2, the pole pieces extend toward each other at theirtips and are separated by an airgap a of a width depending upon thewidth of the ends of the armature,-

to be presently referred to. The tips of the. are cut away to formcurved concave ends 7. The curvature of these ends is preferably in acircle struck up from the axis of rotation of the armature, for a pur-'pose that will presently become clear.

evident that the magnets M and M constitute in effect a single magnethaving a bifurcated north pole 4-4 and a bifurcated south pole 5 5.Although I have referred to the magnets M and M as permanent magnets,they may obviously be in the form of electromagnets.

Between the pole pieces 4 and 4 is mounted acoil C, and between theopposite pole pieces 5 and 5 is arranged a similar coil C. The coils Cand C are connected in series and in eifect constitute a single coil. Itwill As shown in Fig. 2,the 7 It is :ceiaaar be understood, of course,that the coils C and G are properly connected in a suitable telephoneeircuit in which the current varies in accordance with sound wavesintended to be reproduced by the receiver. For convenience I will,therefore, refer to the coils C--U as the telephone coil.

The posts 3 of casting B are preferably so spaced that the magnets withtheir pole pieces and coilsmay be inserted and re .moved as a unitthrough the space between best shown in Fig. 3. The fixed section 8terminates in a conical recess 10, into which fits closely the taperedend of movable section 9. When these correspondingly shaped ends. of thetwo core sections are brought together, they form a continuous ironcore. When the section 9 is moved away from the section 8, an air gap isformed, which decreases the magnetic effect of the coil to an extentdependingupon the width of the air gap, other factors being consideredequal.

This will be understood by those skilled in p the art, without furtherexplanation.

The airgap formed in or at the end of core It, when once adjusted may besaid to be fixed or permanent in that it is notaffected by the vibratorymovements of the armature. In other words, while the airgap between thepole pieces and the vibra tory armature is variable, the controllingairg'ap provided for the core of each coil is stationary and Whollyindependent of the armature airga As faras,I know, this feature isbroadly new, and it may be employedin various combinations in electricinstruments of the telephone type other than Nil) the specificembodiment shown in the drawadapted to engage similar screw-th reads inthe pole piece through which the section passes. Section 9 isprovidedwith an cxtension'in the form of a stub-shaft or arbor 12, preferably ofnon-magnetic bearing material. On the arbor 12 is mounted a smallfine-toothed gear wheel 13, which is so connectedwith the shaft that itrotates the same and yet allows axial movement of the shaft 12 withrespect to the gear wheel. This connection may be formed by providingthe gear wheel '13 with a lug or key 14, arranged to engage in anaxial'slot or groove 15 in shaft 12. In this way, the gear locked to'the shaft so as to rotate the same when the gear wheel is rotated, andat the same time the'gear wheel allows axial movementofthe shaft duetothe screwethreaded mounting of the-core section 9 in the associatedpolepiece. The gear wheel 13 is retated in one directlon or the otherbya-wo'rm 16 formed on or secured to a pin 17, which cally locked inadjusted position against turning and can be operated only through themanually controlled'worm 16.

hen it is desired'to adjust the core see.

tion 9 relatively to the fixed section 8, it N is only necessary to turnthe finger piece 18 one way or the other, until the required adjustmenthas been secured, as the operator will determine from theacousticefi'ect of j the -coil., When the core sections 8 and 9 are incontact with each. other, the magnetic effect of the coil is a maximumand the acoustic eiiect of the instrumentjls correspondingly loud. \Vhenthe core section 9 is separated from the section 8 by an airgap, theultimate acoustic ellect of the coil decreased in a degree'dependingupon the width of the air gap. To inform the operator which way toturn-the finger piece 18, suitable notations may lee-provided on. the.finger piece'and the base 1 to indicatethe loud and'isoft movements ofthe finger piece. The operative connections be tween finger piece-18 andthe movable'.core' section 9 are such as to secure'a very delicateadjustment of the core section, so that the air gap-in the core may beadjusted to a very small fraction of an inch. Theadjoining ends of thecore sections 8 and 9' may he cut of? straight, but I prefer to shapetheni con1cal. so as to secure a better and liner adjustment.owingto theincreased area i of the cone-shaped air gap Between the tips orfrce endsof pole pieces.4--4"and 5 -5 is mounted an armature A. which may simplybe a. short flatlmr of iron ot ihe right size and dimensions,

depending upon the relative arrangement,

and size of the pole pieces- The armature is operatively supportedlietweeuthe pole piecos int.an v practical way. In the drawings I haveshown a U-shaped bracket 21 wheel 13 is always v,atthe. center.

two may be used.

' having a pairof projecting arms 22 and 23'.

between which is pivoted a'stud 24 constructed to hold the armature'A..In Fig.

1, the stud 24; is shown slotted to receive the armature and supportthe'same rigidly mounted on'the base 1 of casting B, as by means ofscrews or bolts 25 passingthrough the lower arm 23 into the base 1(see-Fig. 6). Any other practical mounting for the arma- The armature Ais of such size dimensio'ns' that in its normal position the endsthereof practically span the air gap 0 between each pair of pole pieces,as shown in Fig. 2. If the pole pieces are widerthan (hex-armature, thepolar tips 7 may be reduced to the same width as the armature','asindicated in Fig. 7 This tends to reduce magnetic leakage. Furthermore,the ends of the armatureare so shaped as to move The bracket 21 115firmly in close proximity past the curved tipsrfof the pole pieces 44'and 5-5'.without' acair gap between the pole tips-7 and the armature isalways maintained at a minitually touching the same. In this way'the Iwide its arc ofvibration under the influence of coil C I Also',it shouldbe noted that the adjustment of either core section has no effect on thenormal magnetic flux, so that an air gap produced in the core does notincrease thereluctance of the path traversed by the flux otmagnetM-MT.As will be clear from F 2, the construction of field magnet and armatureis such that there is practically no magnetic leakage. This arrangementproduces an instrument of high sensitivity and efficiency. The clearancebe-. tween thecorrespondingly .curved polar tips 7 and the ends of thearmature maybe made. assmall asmechanical' conditions permit. Thisminimum air gap, which yet makes it impossible for the armature torattle against the pole pieces, causes a weak current in coil CC' toproduce a maxinun'u' response of the armature. 'lVhen both coils on thearmature' There is no shuntinp or diverting of any part bf the normalfield flux from the operative air gap between the pole pieces and thearmature. This constanmaintenance of the normal magnetic field at fullstrength in its relation to the-armature causes minute currentvariations in the C and G are used the are sowo-und that speaking coilor coils to produce a maximum etiect on the armature, thereby impartlngto the instrument a high degree t sensitivity. The practical value ofanormally' the speaking coil, react strongly on the ar-' mature. When I'say that the armature is always subject to the full strength of thenormal magnetic field, and that the magnetic regulating device for theflux of the coil does not divert or shunt any portion of the normalmagnetic held from the armature, -I do not mean that the normal field.

flux passes through the length of the armature as shown in theillustration of Fig. 2. l simplymean that practically the full strengthof the magnetic field is always exerted on the vibratory armature acrossthe operative air gap or air gaps, irrespective oi any particulararrangement of magnet and armature. 0f course, it will beunder stoodthat due. allowance is made for such magnetic leakage or losses ascannot possibly be avoided in the mechanical construction of theinvention, no matter how carefully carried out.

On the ring f casting B is mounted an acoustic diaphragm D of properdesign and material. There are many-kinds and styles of diaphragms onthe market suitable for this purpose. The most common material of whichthese diaphragms are made is mica, which is moisture-proof and gives astrong reproduction. Some peopleprefer a diaphragm of wood, especiallymaple, which gives a more pleasing reproduction than mica, thoughperhaps notso strong.

Diaphragm D is held in place on the ring 2 in any practical way. In theembodiment shown inthe drawings, the supporting ring 2 has aninwardlyprojecting shoulder or flange 26- and a screw-threaded wall 27.

--The diaphragm is clamped firmly in osition by a. screw-threaded ring28. t is preferable to clamp the diaphragm between a pair of washers 29of -felt, leather, rubber,

' or other sound-absorbing material.

crank com rising along arm 33 and a short. 'arm 34. he free end of thelong arm 33 is To the ring 2.is fixed a bracket 30 having a pair ofspaced lugs 31", between which is pivoted at32 a lever indicated as awhole by'L. This lever is in the form of a bel-l D, as indicated at 35in Fig. 1. The short arm 34 of lever "L is provided with a lateralextension 36, "which may be an integral part of the lever. The free endof the extension 36 is connected to the armature A by a rod or stiffwire 37,-or any other practical means. The point at which the rod 37 isConnected to thearmature depends upon the amplifying ratio which it isdesired to the lengths of the arms 33 and 3d of lever L,

any desired leveragebetween the armature and the diaphragm can besecured. These calculations are well. within the skill of the manconversant with this art.

In Figs. 8 and 9, I have shown a modified form of connection between thearmature.

and the diaphragm. In this construction, the connecting lever, indicatedas a whole by L, comprises a long arm 38, a lateral extension 39 and anadjustable short arm indicated as a whole by J. This arm comprises apair of short rods or pins 40 and 4E1, which are. adjustably connectedtogether through an oppositely screw-threaded nut 42. The ends of thepins 40 and 4:1 are in screw-threaded engagementwith this nut, and byturning the nut one way or the other, the pins are drawn closer togetheror forced apart. In this way the effective leverage between the pivotpoint 82' and the lower end of the arm J can be adjusted as required.The arm J is at its lower end connected to the armature through asuitable link 4:3, which may be a -stitl wire or any other practicalconnection. The adjustable lever L is applicable in the constructionshown in Figs. 1 and 2, and to avoid re etition of drawings, it will beunderstoo that the lever L may be substitutedfor the lever Ii.

Although I have shown a specific form of adjustable arm J, it is clearthat in the broad aspect of my invention there are various ways ofcarrying out this idea, and

' Figs. 8 and 9 are, therefore, to be considered as merely illustrative.

The support or casting, B, which carries the operative parts of my newloudspeaking telephonereceiver, is preferably constructed to be insertedas a umt into-an outer casing. In Fig. 1, there is anouter'casing orhousing indicated as' a whole by K. This casing may be cast or molded asa single piece of any suitable material, such as bakelite, aluminum andthe like. Casing or housing K is of proper size and design to receivethe casting B and all parts carried thereby. The lower inner end ofcasing K is screwthreaded to receive the screw-threaded section 44 ofcasting B, which thus forms a cap or housing for the lower end of thecas-' ing. To permit easy manipulation of casting B in screwing it intoor out of the casing K, the base 1- of the casting may be formed with asli htly projecting flan e or rib 45, which is easily grasped by thefiri gers. 4130 When the casting B is properly screwed into the outercasing K, the top of ring 2'and annular clamping ring 28 rests against-ashoulder 46 formed inside of the casing, as shown in Fig. 1. i

The top. of outer casing K-is provided with a. centralopening which issurrounded by a flange or extension 47 adapted -,to receive theinner'end of a born 48 For this purpose the extension 47 may be madeslightly cone-shaped, so as to provide a tight fit for the born. Whenthe outer casing K is used to support a horn 48, the-casing is mountedon a suitable base or stand T,

which is provided with anopening 49 of proper size'to rec'eive casing K.As seen in Fig. 1, the casing has,an annular shoulder 50 which restsontop of the stand T. Casing K fits snugly and firmly into the stand '1without the necessity of; any fastening devices. The frictional securingmeans thus formed by the snugly engaging surfaces of base T and easing Kis sufficient to hold the casing rigidly .on its supporting base. To

remove the casing K and all parts carried thereby, it is only necessaryto. separate it fromthe stand T, which is easilydonewithout the use oftools. The instrument may be used without the stand T, as when it isdesired to connect it to a phonograph horn embodied in a cabinet; Inthat case the extension 47 on the cover of casingK is so shaped as tofit over the small end of a mounted horn.

In Fig. 10 I have shown a slightly modified form of outer casing andsupport for the operative parts. The outer casing K is preferably castormolded in a single piece and also constitutes the stand or base forthe instrument. vI'n other words, the outer casing K and a stand '53.The cylindrical portion 52, of the cover has screw-threads 54 arranged-to' engage corresponding screwthreads 55 of a support indicated as awhole by B". The support B is generally similar to the support B.previously described in detail, and is adapted to'carry the operativeparts in the same way as described in "connection with. support B. I

Although I have shown and described the magnet M.N 'as provided with twocoils C and C, in the broader aspect of my invention it is sufficient ifonly one coil is used.

In that case, the other pole piece would be solid and not bifurcated.Personally, I prefer t0 use a coil for each end of the' armature, so asto secure the greatest effect with a'weak current.

The operation of my new receiver will be clear to anyone skilled in theart and I need not, therefore, go into any details on this point, I needonly say that normally the armature A is held in a neutral or balancedposition between the tips of the pole pieces,

consists of a cover "51, a cylindrical wall 52,

effect of the coils and the armature vibrates ,in a manner wellunderstood. These vibrations are in accordance with thecurrent vari-.ations in the coil and are transmitted in increased ratio through theconnections previously described. In this way, the smallest vibrationsofthe armature are repeated by the diaphragm in magnified movements, so

that the sound produced ma be heard at a distance.

While I have herein shown and described a specific form of magneticstructure and armature arrangement, I want to make it clear that I havedone so merely by way of example'and that the feature of adjusting .themagnetic effect of the coil 0n the armature can be used with any otherpractical construction of magnet and the vibratory member operatedthereby. v

In the broaderaspect of my invention, the particular means for varyingthe effect of the telephone coil independently of the air' gap betweenthe armature and the pole pieces, may be carried out in other practicalWays than the one herein shown and de scribed for the sake ofillustration. For instance, t his feature of my invention can be used ina construction where the armature is in the form of a diaphragm ofmagnetic material "ence of the coil.

phragm D is not necessary. Therefore, in the claims, when I mentlon anarmature Without reference to a diaphragm, I'mean broadl any movablemagnetic member arranged to be. influenced by the magnet. When Imagnetic effect of. the coil, I .do not, of course, mean the variationsproduced by the variable current in the coil, since those varia tionsare automatic and beyond the control of the user of the instrument.

In radio reception, broadcast programs vary all the way from thereporting of sport-v ing events to the rendition of music by bands andorchestras. The same loudspeaker will [usually not reproduce all ofthese diflerent numbers satisfactorily without adjustment or regulationof the magnetic effect of the coil in the loudspeaker. \Vhen a person desires a loud number on a program reproduced softly, he adjusts theloudspeaker to decrease the magnetic efiect of the coil on the armature.'In the particular instance illustrated in the drawings, this is done byturning the finger piece 18 in a direction to produce an air gap betweenthe core sections by the diaphragm adapted to vibrate under the influ-In such a case theJdiaspeak of varying or adjusting the 8 and 9. On theother hand, when, for instance, a violin solo is broadcast, theinstrument would probably be adjusted to give out a maximum volume ofsound. This would be effected by closing the air gap between the coresections 8 and 9, in the particular construction shown in the drawings.

Either core or both cores B may be adjustable. For simplicity, I haveshown each core adjustable independently of the other,

while the pole pieces are made of a material of high permeability."-Expressing this difrents.

ferently, the retentivity of the pole pieces and coreis lower than thatof the steel body of the magnet. It is well known that the steel orsteel alloy used for permanent magnets is hard steel, so. as to retainthe magnetization. The high retentivity of hard steel causes it to beless susceptible to'variations in the magnetizing or demagnetizingforce. Hence, in those prior telephone receivers where flux variationsdue to variable impulses in the talking coil must pass through the bodyof the permanent body, the efficiency of the instrument is lowered,because the steel mass of the magnet offers considerable resistance toflux variations, and this resistance increases with increased frequencyof the variable magnetizing cur- This objection and disadvantage isobviated in aconstruction embodying my invention, where the fluxvariations produced by coil C or C take place only in the associatedpole pieces and core outside the steel mass of the magnet. In otherwords, variations in magnetic fiux'are confined to a path of highpermeability, so that variable impulses in the telephone coil produce'flux changes with minimum loss and maximum efiiciency. Y

Although I have herein shown and described, certain specificconstructions, I- would have it understood that I have done so for thesake of explaining my invention to those skilled in the art, and not byway of restriction or limitation' It will be apparent that the variousfeatures of my invention may be mechanically embodied-in other formsthan herein set forth. As far as I know, I am the first to provide atelephone instrument in which the magnetic effeet of the telephone coilis controlled without changing the normalair gap between the magnet andthe armature, and without diverting or shunting any portion of thenormal magnetic field from the armature.

As previously explained, the per- Hence, way. I may add that in thedrawings I have not attempted to show the operative parts inmathematically calculated proportions, since therelative sizes anddimensions of those partswill vary in different embodiments of theinvention, and also since the (orrect design of the instrument in eachcase isreadily determined by the man skilled in this art.

It will be understood that, although the illustrative embodiment shownin the drawings has been described as a telephone receiver, the variousfeatures of my invention are equally'applicable in various otherelectrical instruments of that type.

I claim as my invention: 1. In a telephone receiver, 'a magnet, avibratory armature operatively associated with thepoles of said magnet,a coil for causing vibration of said armature, and manually controlledmeans for regulating the magnetic effect of saidcoil on the normal fieldof said magnet independently magnetpoles, .said regulating means beingarranged to operate without diverting any portion of the normal magneticfield from the armature. 2. In a telephone receiver, a magnet, avibratory armature operatively associated with the poles of said magnet,a coil for causing vibration of said armature, and manually controlledmeans for varying the reluctance of the magnetic circuit produced bysaid coilwithout varying the air gap between the, armature and themagnet poles, said regulating means being arranged to operate withoutdiverting any portion of the normal magnetic field from the armature.

3. In a telephone receiver, a magnet, a

I claim this idea in a fundamental fil of the air gap betweenthearmature and the vibratory armature operatively associated with thepoles of said magnet, a coil for causing vibration of said armature, amagnetic core for said coil, said core being arranged outside the normalflux path of said magnet so as not to divert any portion of the normalmagnetic field from the armature, and means for varying the magneticpermeability of said core, whereby the magnetic effect of said coil onthe field of said magnet and therefore on the armature is variedaccordingly.

4. In a telephone receiver, a magnet, 21 vibratory armature operativelyassociated with the poles of said magnet, a coil for causing vibrationof said armature, a magnetic core for said coil, said core Cons sting ofseparable sections arranged outside the normal ilux path of said magnetso as not to divert any portion of the normal magnetic field ;'from thearmature and means for adjusting one section relatively to the other forvarying the magnetic effect of sad coil on said armature.

5. In a telephone receiver, a magnet having oppositely arranged polepieces, one of said pole pieces consisting of a par of spaced-limbsorbifurcations, a magnetic (ore connecting the limbs of said bifurcatedpole piece, a vibratory armature operatively assoc ated with saidp'olepieces, a coil on said core to cause vlbratlon of said arma ture,means for-regulating the -magnetic -effeet of said coll on the normalfield of said magnet, independently of the air gap be a coil on saidcore to cause vibration of said fl'armature, means for varying themagnetic permeab'lity of said corewithout-diverting any portion of thenormal magnetic field from the armature and thereby controlling themagnetic efi'ect of said coil on the nor- 9 mal field of said magnet,and an acoustic member controlled by said armature.

7. In a telephone receiver, a magnet having oppositely arrangedpolepieces, one of spaced limbs or bifurcations, a magnetic core connectingthe limbs of said bifurcated pole piece, said core consisting ofseparable sections arranged outs'de the normal flux path of said magnetso as not to divert any 0 portion of the'normal magnetic field from thearmature, a v'bratory armature operatively associated with said polepieces, a coilon said core tocause vibration of sad armature, means foradjusting one core section relatively to the other for varying the amagnetic efiect of said coil onsaid armature, and an acoustic membercontrolled by s'aid armature. v

' 8. In a telephone receiver, a magnet having pole pieces, a vibratoryarmature-mounted in operative relation to said 'pole' pieces,

the ends of said armature being separated from the respectivepore-pieces by a practically minimum air. gap and arranged to 5 movepast the polar faces of the pole pieces W'thout striking said polepieces during the maximum vibrations of the armature, a coil forcausingvibration of said armature, means for varying the magnetic effect ofsaid coil on the normalfield of said magnet Withoutvary'ng said minimumair gap and Without divertingany portion of the normal magnetic fieldfrom the armature, and arr acoustic member controlled by said. ar- 5mature. I I

'said pole pieces cons'sting of a pair of 9. In a telephone receiver, a"magnet having pole pieces, a vibratoryarmature mounted in operativerelat on to sald pole pieces,

the ends of said armature being separated from the respective polepieces by a practically minimum air gap and arranged to move past thepolar faces of the pole pieces Without striking sa'd pole piecesduringthe 'maximum vibrations of the armature, a coil for causingvibration of said armature, manually controlled means for varying thereluctance of the magnetic circu t produced by said coil without varyingsaid minimum air gap and Without diverting any portion of the normalmagnet c field from the armature, and an acoustic member controlled bysaid armature.

10.: In a telephone receiver, a magnet having pole pieces, a vibratoryarmature mounted in operative relation. to said pole pieces, the ends ofsaid armature being separated from the respective pole pieces by apracti cally minimum air gap and arranged to move past the polar facesof the pole pieces without striking said pole pieces during the maximumvibrations of the armature, a col for causing vibration of saidarmature, a magnetic core for said coil, said core being arrangedoutside the normal flux path of said magnet so as -not to dlvert anyportion of the normal magnetic field from the armature', meansfforvarying the magnetic. permeability ofs'aid core to regulate the 'magnetic effect of said coil on the armature independently of said air gap,and an acoustic member controlled by sa d armature.

11. In a telephone receiver, a magnet, a

.vibratory armature extending between the poles of said magnet, a coilfor causing vi- 'bration ofsaid armature, and means for regulating themagnetic effect of said coil on said armature without varying the normalpath of the flux of said magnet across the air gap between the magnetpoles and the armature.

12. In a telephone receiver, a vibratory armature operatively supportedin a magnetic field, an acoustic member, means for so connecting saidacousticmember.with said armature that the vibrations of the armatureare transmitted in increased ratio to said acoustic member, saidconnections including a device supported on a fixed pivot,

and manually operable means for adjusting said connecting device tovary" the trans-' mission ratio between said armature and said member."

13. Ina telephone receiver, a vibratory armature operatively supportedin a magnetic field, an acoustic member, connections between saidarmature and said member for transmitting the vibrations of the armaturein increased ratio to said member, said connections including an armsupported on a fixed pivot and means for varying the efl'ective leverageotsaid arm to vary the transmission ratio between said armature and saidmember.

141. In: a telephone receiver, 'an acoustic diaphragm, a pivotedbell-crank lever having a long arm and a short arm, means for connectingthe free end of said long arm with the center of said diaphragm, avibrating armature operatively mounted in a magnetic field, means forpivotally supporting said armature independently of said lever,

and means for connectlng the free end of said'short arm to saidarmature, whereby the Vibrations of said armature are transmitted tosaid diaphragm in increased ratio.

15. In a telephone rcce'ver, an acoustic diaphragm, a vibrating armatureoperatively mounted in a magnetic field, a pivoted bell crank leverhaving a long arm and a short arm, means for supporting said armatureindependently of said lever, means for connecting the tree endof saidlong arm with the center of said diaphragm, means for connecting thefree end of said short arm to said armature, whereby the vbrations of,said armature'are transmitted to said diaphragm in increased ratio, andmeans for adjusting the effective lengthof said short arm.

16. In a loud-speaking telephone receiver, 'anouter casing having acylindrical section provided with a screw-threaded port-on, a

support removably fitting into said cylindrical section and held inplace by said screw-threaded portion, said support comprising a base anda rin an acoustic diaphragm mounted on'sai r1ng,electrom agnetic'mechanism including a vibratory arcarried thereby constitutin maturemountedon said base, and an operative connection between said diaphragmand said armature, said support and all parts a unit insertable into andremovable from said outer casing. v .1

17. In a telephone receiver, a pair of magnets having their like polesarranged oppositely and spaced from each other, a polar projectionextending from each pole, the polar projectionsoi each pair of like"poles constituting a. bifurcated pole piece having an air gap betweenthe free ends of the pro-,

jections, a vibratory armature normally held substantially in alignmentwiththe air gaps of said polar projections, a magnetic core arrangedbetween each pair of polar projections, a coil on each core for causingvibrajections, a'vibratory armature normally held substantially inalignment with the air gaps of said polar projections, a magnetic corearranged between each pair of polar projections, a coil on each core forcausing vibration of said armature, manually adjustable means forcontrolling the magnetic eifcct of one or both coils on said-armature,and a diaphragm operatively connected to said armature.

19. In a telephone receiver, a pair of mag:

nets having their like poles arranged oppositely and spaced from eachother, a polar projection extending. from each pole, the polarprojections of each pair of like poles constituting a bifurcated polepiece having an air gap between the free ends of the projections, avibratory armature normally held substantially in alignment with the airgaps of said polar projections, a magnetic core arranged between eachpair of polar projections, a coil on each core for causing vibration ofsaid armature, manually operable means for varying the reluctance of themagnetic circuits produced by said coils without adjusting the air gapsof said polar projections, and a diaphragm operatively connected to saidarmature.

20. In a telephone receiver, a pair of magnets having their like polesarranged oppositely and spaced from each other, a polar projectionextending from each pole, the

polar pro ections of each pair of like poles constituting abifurcatedpole piece having "an air gap between the free ends of theprojections, a vibratory armature extending lengthwise between the airgaps of said polar projections, an adjustable magnetic core arrangedbetween each pair of polar pro ections, a 0011 on each core for causingvibration of said armature, means for ad 'justing said cores to vary themagnetic effect of said coils on'the' armature, andv a diaphragmoperatively connected to said arma- .coil for causing vibration of saidarmature,

and an adjustable core extending through said coil for regulating themagnetic ell'eci of said coil on said armature independently of. saidpole pieces. I

22. lln an electric instrument. a magnet having pole pieces, a vibratoryarmature operatively associated WltllSLllLl pole pieces, there being anoperative air gap between the armatureand the magnet, a coil operativelyassociated with said armature, a magnetic core for said coil,and meansfor varying the magnetic permeability of said core independently of saidair gap, whereby the movements of said armature do not a'll'ect theadjusted permeability of the core.

23. in an electric instrument, a magnet zvided with a magnetic lyassociated with said. armature, a magnetic core for said coil, and meansfor producing an adjustable air. gap in the core independently of saidoperative air gap, wherebythe movements of said armature do the adjustedair gap in the core.

24. In an electric instrument, amagnet having pole pieces, an'armatureoperatively associated with said pole-pieces and separated therefrom byan air gap, and a coil procore consisting of sections Which arerelatively adjustable inpieces and said air gap, whereby the movementsof said armature have no effect c of said sections.

25. In an electric instrument having a magnet and a movable armature, acoil having a magnetic core, and controllable means for producing anadjustable air gap in said core and malntaining said air gap as ad-;

justed independently of the movements of said armature.

26. In an electric instrument having a movable magnetic armature, a coilprovided with a magnetic core consisting of relatively adjustablesections for producing a variable air gap therebetween, andmeans formounting said sections independently of said armature.

27. In a telephone receiver, a magnet having a bifurcated pole piece, anarmature operatively associated with said ma net, a magnetic corebetween the bifurcations of said pole piece, a coil on said core, and

, means for varying the magnetic permeability of said core to controlthe magnetic effect of said coil on the flux passing through saidbifurcations and the armature.

28. In a telephone receiver a magnet, a movable armature operativelyassociated with said magnet, a coil for controlling said armature, andadjustable magnetic means arranged outside the normal flux path of saidmagnet for controlling the "magnetic elfect of said coil on saidarmatureindependently of the normal air gap between the magnet and the armature.

29. In a telephone receiver, a magnet for maintaining a normal magneticfield, said magnet having pole pieces,'a movable magnetic memberoperatively associated l w1th said pole pieces, a coil for controllingthe operation -of said member, and ad ustable magneticfmeans independentof sa d pole piecesumd said member for controlling the reluctance of themagnetic circuit of said coil.

30. In a loudspeaker, a magnet structure having four pole pieces, likepoles being arnot disturb v having pole pieces,

on the adjusted position lever at the junction diaphragm, and an amagnetic bar pair of spaced like poles, separate from the main a coilmounted on each bar I between like poles, whereby the normal field fluxdoes not pass through said coils, and acoustic means operated by thecombined action of said magnet and coils.

31. In a' telephone instrument, a magnet one of said pole pieces beingbifurcated, an armature operatively associated with said pole pieces, amagnetic core connecting the limbs of said bifurcated polepiece andarranged outside the normal flux path of'said magnet, and a coil SU1'-32. A telephone instrument comprising a rounding said core.

pair of magnets having their poles arranged oppositely and spaced fromeach other, a

polar projection extending from each pole,

the polar projections of each pair of like oles constituting. abifurcated pole piece aving an air gap between thefree ends ofthe'projections, a vibratory armature operatively associated with saidpolar projectrons, a magnetic core arranged between each pair of polarpro ections, a coil on each core, and-a diaphragm operatively connectedwith said armature.

33. In a telephone instrument, a base, a magnet mounted on said base, anarmature operatively associated with said magnet, an acoustic diaphragmmounted substantially parallel with said base, a bell-crank leverconsisting of a long arm'and a short arm, both of said arms beingseparate from said armature, means for freely pivoting said securing thefree end of said long arm to said diaphragm, and means for connectinrsaid armature to said short arm, whereby the movements of said armatureare transmitted to said diaphragm in increased ratio.

34. In a telephone instrument, a pivoted bell-crank lever consisting ofmeans for conneeting the 'free end of said long arm with said diaphragm,a vibratory armature mounted in a magnetic field and arranged to vibratein a plane substantially perpendicularto the plane or axis of vibrationof said operative connection be tween said armature and the short arm ofsaid lever.

35. In an electric instrument, a magnetic system including an adjustablebar to regulate certain flux values of said system, means for supportingsaid bar for combined rotary and axial movement to adjust its positionrelatively to a fixed part of said system, a gear mounted on said bar torotate the same and thereby cause axial adjustment of said bar, theconnection between said gear and said bar permitting axial movement ofthe of'said arms, means for latter, a worm for operating said gear, anda manually operable member for actuating said worm.

' '36. In an electric instrument, a magnetic system including anadjustable bar to regulate certain flux values of said system, means vforjsupporting said bar for combined rotary and axial-movement to adjustits position relatively to a fixed part of said system, a

member for rotating said bar and therebyv adjusting the same axially,asecond member engaging said first member for operating the latter, theengagement between said members automatically locking said bar inadjusted position and positively preventing movement of said bar exceptthrough said second member, and means for controlling said secondmember.

37. In an electric instrument, a base, a magnet mounted on said base, anadjustable magnetic bar associated with said magnet, means for mountingsaid bar for combined rotary and axial movement relatively to saidmagnet, a hand-operable rotary member extending throughsaid base andaccessible from outside the instrument, and a micrometer. drivingconnection between said bar and said member for imparting simultaneousrotary and axial movement to said bar in, either direction. y

38. In an electric instrument, a magnet, an armature operativelyassociated with said magnet, a coil for causing vibration of saidarmature, a magnetic core for said coil, said core consisting of a fixedsection and an axially adjustable section, the. adjacent ends of saidsections being respectively in the shape of a conical recess and aconical extension to provide a cone-shaped air gap between saidsections, and means for adjusting the second section relatively to thefixed section for varying the Width of said air gap.

39. In an electric instrument having a movable magnetic armature, a coilprovided with a magnetic coreconsisting of relatively adjustablesections for producing a variable air gap therebetween, the adjacentends of said sections being respectively in the shape of a conicalrecess and a conical extension to provide a cone-shaped air gap betweensaid' sections, and means whereby said air gap is maintained as adjustedindependently of the movements of said armature.

etO. In a telephone receiver, a magnet structure comprising a pair ofbifurcated pole pieces oppositely arranged, a vibratory armature mountedin operative relation to said polepieces, a magnetic core arrangedbetween each pair of bifurcations so as to be outside the normal fluxpath of said magnet, a coil on each core for controlling the vibrationof said armature, and a diaphragm operated by said armature. f

41. In a telephone receiver, a magnet structure comprising a pair ofbifurcated pole pieces oppositely arranged, a vibratory armature mountedin operative relation to said pol'e'picces, a magnetic core arrangedbetween each. pair of bifurcations, a coil on each core for controllingthe vibration of said armature, manually adjustable means forcontrolling the magnetic effect of ,one or both coils on said armature,and a (liaphragm operated by said armature.

421111 a telephone receiver, a magnet structure comprising a pair ofbifurcated pole pieces oppositely arranged, a vibratory armaturemountedin operative relation to said pole pieces, a 1nagnctic.core arrangedbetween each pair of bifiu'cations, a coil on each core for controllingthe vibration of said armature, manually operable means for varying thereluctance of the magnetic circuits produced by said coils withoutadjusting the normal air gap between said pole pieces and said armature,and a diaphragm operated by said armature.

43.,In a telephone receiver, a magnet structure comprising a pair'ofbifurcated pole pieces oppositely arranged, a vibratory armature mountedin operative relation to said pole pieces, a magnetic core arrangedbetween each pair of bifurcations, a coil on each core for controllingthe vibration of said armature, means for adjusting said cores to varythe magnetic effect of said coils on the armature, and a diaphragmoperated by said armature. I

44.. In a telephone instrument, a magnet having a vibratory armature, adiaphragm,

a lever mounted between its ends on a-tixed' pivot, one end of saidlever being connected to said diaphragm and the other end to saidarmature, and means for adjusting the effective length of said leverbetween its pivot and one end thereof to vary the transmission ratiobetween said armature and said diaphragm.

45. In a telephone instrument, a magnet, a vibratory magnetic memberoperatively associated with said magnet,- there being an operative airgap between said magnet and said member, a pair-of coils operativelyassociated with said vibratory member, and a magnetic core for'eachcoil, the magnetic circuit of each coil having a predetermined fixed airgap separate from said operative air gap.

46. In a loudspeaker, a pair of permanent magnets arranged with theirlike poles in spaced relation, an iron bar connecting each pair of likepoles, a coil mounted on each bar between like poles, so that the normalfield flux does not pass through said coils, and acoustic means operatedby the combined action of said magnets and coils.

47. In an electric instrument of the telephone type, a magnet structurehaving rigid pole pieces connected by a pair of magnetic cores, therebeing a predetermined fixed airlll) ' magnet having a predeterminedairgap,

gap 1501' each core to provide a magnetic path of predeterminedreluctance through each core,.a coil on each core, and a vibratorymagnetic member in operative relation to said pole pieces, the airgapsin said magnetic paths through the cores being independent of thevariable airgap between' said pole pieces and said vibratory member.

magnet, pole pieces attached to said magnet in magnetic contacttherewith and having means to provide a magnetic path with being ofgreater permeability than said permanent magnet and including said polepieces in series, a coil in said magnetic path H between the polepieces,

i member in operative relation to said magnet and coil.

and a vibratory 49.1n a telephone receiver, a permanent pole piecesofgreater permeability than the magnet itself, said pole said magneticpath pieces being in-- magneticcontact with said magnet, a coilassociated with said pole piecesior producing a varying flux, meanswhereby the flux variations occur in a path including said pole piecesand a predeter-Y saidpath'beingout-v mined airgap in series, side themass of said permanent magnet, and

p a vibratory member controlled by said flux 48. In a telephonereceiver, a permanent variations, said independent of said member.' v

50. 'In atelephone-receiver, having a permanent magnet, va polarattachment for said predetermined airgap being the vibratory movementsof magnet comprising a, pair of pole pieces con nected by atransverse-magnetic'core carrying a coil, said core within said coil,and a vibratory magnetic memberin operative relation to said magnet andcoil, said pole pieces and core forming a variable magnetic circuit ofgreater permeability than said permanent ma net.

providing an airgap ,ADOLPH AaTHMAS.

